Approximately 93% of motors constructed use iron cores, or variations thereof, to concentrate magnetic flux and boost torque. “Coreless” motors are suited for very high RPM's with low torque and iron core motors usually utilize insulated steel laminations in their stators which reduce heat losses from eddy currents. However, even with thinner laminations, the eddy currents are only blocked in one plane. So to further reduce eddy current losses, silicon is typically added to the steel to reduce its electrical conductivity. Although the silicon reduces some remaining eddy current losses (by reducing the current conductivity), the addition of silicon actually worsens the magnetic conductivity. This reduction of magnetic strength reduces the maximum amount of torque produced, and also reduces electrical efficiency.
Most prior art multi-phase motors use phase windings radially sequenced around the plane of rotation. The close coupled proximity results in “Armature Effect” which reduces efficiency at higher speeds. The usual multi-phase high speed motors also require a gearbox or other loss prone speed reducing device in order to boost torque. Additionally, conventional motors use some variation of axial or radial flux, with multiple salient windings wound around iron type cores. Although this boosts magnetic flux, it also increases inductance and electrical resistance, and reactance. At higher speeds, the inductive and reactive losses limit top speed and efficiency at high speed.
Known prior art direct drive motors include U.S. Pat. No. 4,625,392 issued to Stokes on Dec. 2, 1986 titled Method of manufacturing a molded rotatable assembly for dynamoelectric machines describes molding a rotor of a motor from magnetic material. However, it does not involve Transverse Flux and does not use molded material for the stator.
U.S. Pat. No. 4,853,567 titled Direct Drive Motor issued on Aug. 1, 1989, which describes a three phase outer rotor motor. However, it uses conventional configuration with the three phase windings sequentially located within the same axis, and does not use Transverse Flux.
U.S. Pat. No. 5,777,413 issued to Lange et al. on Jul. 7, 1999 titled Transverse flux motor with magnetic floor gap describes a locomotive motor with Transverse Flux. However, it uses conventional iron laminations as its flux path, and is mainly concerned with physically flattening the motor to allow it to fit into the space between the floor of the locomotive and the train axle.
Prior art transverse Flux motors have historically been too costly to construct, and have rarely been used. This invention simplifies construction and lowers costs of Transverse Flux motors, and at the same time increases electrical efficiency to a higher level than before.
U.S. Patent Application No. 2006/0208602 filed on Mar. 16, 2006 to Enomoto teaches a multiple phase claw pole type motor which includes a plurality of claw poles facing a rotor in a state of being separated from the rotor by a small gap, a radial yoke extending radially outwardly from this claw, and an outer peripheral, yoke extending from this radial yoke portion in the same direction as the direction of extension of the claw portion, a stator core formed by alternately placing the claw poles in a circumferential direction so that a distal end of each claw portion faces the outer peripheral yoke of an adjacent one of the claw poles, and a stator constructed by sandwiching an annular coil with the adjacent claw poles of this stator core, a multiple phase claw pole type motor characterized in that the claw poles are formed by compacting a magnetic powder and are formed of a magnetic compact having a DC magnetizing property.
The differences between the “claw pole” and the parallel pole motor is that claw pole motors have been around since the 1930's and have fatal disadvantages including that they are extremely inefficient—typical values of efficiency are 45-65%; they are limited in torque; eddy currents are very high and fringing losses are very high. Most applications use “claw” shaped poles in an attempt to minimize this loss. That trapezoidal shape of poles however, further limits torque.
Unlike Enomoto, U.S. patent application Ser. No. 11/731,427 filed on Mar. 30, 2007, now U.S. Pat. No. 7,492,074 issued on Feb. 17, 2009 to Rittenhouse, describes a direct drive motor, not a claw pole motor. The Rittenhouse '074 direct drive motor overcame a problem with prior art motors by using separate, independent, uncoupled planes for each phase, and phase and pulse timing to eliminate the “Armature Effect” which results is much higher efficiency at higher speed. The motor also has very high torque and can drive directly most loads without requiring clutches, gearboxes, or other speed reducing devices. The result is greater efficiency, lower costs, and fewer moving parts.
The Rittenhouse '074 patent also overcomes prior problems associated with boosting magnetic flux, which increases inductance and resistance and at higher speeds; the inductive losses limit top speed and efficiency at high speed. The direct drive motor of the present invention can use radial flux construction, but the preferred embodiment is Transverse Flux construction. In Transverse Flux construction, one large single winding powers each phase. Because magnetic flux is directly proportional to Ampere-Turns, the same magnetic flux can be achieved with more turns with less amperage, or higher amperage and fewer turns. In the preferred embodiment, this novel motor has fewer turns, and higher amperages. With fewer turns, the inductance is less, and with larger copper conductors the electrical resistance is also less. Since the inductance and resistance are reduced, both the inductive losses and the resistive losses are greatly reduced which results in higher efficiency and a much higher usable speed range. However, performance and cost of Neodymium-iron-boron permanent magnets have increased since the development and filing of the Rittenhouse '074 patent.
What is needed is a direct drive motor that uses less magnetic weight and still has the same performance that can be three stator or one single stator. Also needed is a direct drive motor having an overall weight that is reduced by over half, uses improved magnetic flux pole pieces shaped for a simplified, shortened magnetic path.